Background: Individuals with Prader-Willi syndrome (PWS) are at increased risk for mental health and behaviour problems, such as skin-picking and compulsive behaviours. Prevalence and functional assessment of skin-picking, and its association with compulsive behaviour and self-injury, were investigated in a large group of individuals with PWS (n = 119). Materials and Methods: Data on demographic characteristics, skin-picking and compulsive and self-injurious behaviours were collected by questionnaires. Behavioural function of skin-picking was assessed by administering the "Questions About Behavioral Function" scale. Results: Skin-picking was found in 86% of the sample, and correlated positively with compulsive behaviours. No associations were found between skin-picking and other variables. Functional assessment suggest that in most cases (i.e. 70%) skin-picking primarily had non-social functions. Conclusions: Skin-picking and compulsive behaviours are common in PWS. In most cases, skin-picking may be maintained by contingent arousal reduction. Controlled studies on behavioural treatment are lacking. Implications for treatment selection are discussed.